ALMA
(Association of Loudspeaker Manufacturing & Acoustics
International)
is a 51-year-old not-for-profit trade association dedicated to the design, test
and manufacture of speakers. ALMA's annual Winter Symposium, held in Las
Vegas, NV, the two days before CES, comprises seminars, papers, tutorials and a
small exhibit area where finished speakers, speaker parts and materials, design
and test tools were on display. ALMA offers high-quality program material and
access to leading engineers in the audio business.

Floyd Toole and Sean Olive are the Lennon and McCartney of
speaker measurements — the pair coauthoring a prolific string of hit AES
papers over more than two decades. Their rigorous research has significantly
advanced the industry's understanding of how to use trained listeners with
normal hearing to subjectively test speaker performance and preferability
correlating those results with speaker design targets that likely will lead to
higher consumer acceptance.

With the last decade's growth of portable audio hardware and
the iTunes ecosystem, and more recently smartphones with music-player features,
the headphone market has radically expanded. The time is right for new research
to do for headphones what Toole and Olive did for speakers. However, headphones
come in several distinct varieties (over the ear, on the ear, and in the ear)
and ears vary significantly from person to person. Plus, consumers want devices
that are both comfortable and increasingly fashionable. So the task is not easy.

Harman's Sean Olive and Todd Welti reported on the
relationship between headphones' perceived and measured sound-quality. The
goal was to find a set of acoustical measurements that correlate and predict
trained-listener sound quality ratings. "The current state of headphone
measurement research does not lend itself to consensus on what the ideal target
frequency response should be … because the scientific research has not been
done to identify it." They found that a flat "perceived spectral balance"
was the most preferred.

An additional paper on headphones by CJS Labs' Christopher
Struck gave a good overview of headphone and headset acoustics. Struck reviewed
the basic concepts underlying headphone and headset measurements, and the
various types of fixtures used in such tests.

Steve Temme, Pascal Brunet and Parastoo Qarabaqi (Listen) presented on measurement of harmonic distortion
audibility, using a simplified psychoacoustic model. This is important because
engineers should focus on fixing the distortion problems that are perceptually
most significant to the listener. Listen's Perceptual THD measurement is based
on the PEAQ (perceptual evaluation of audio quality; Wikipedia)
from the ITU, which models mean opinion scores (MOS) as used in telecom testing.

As the speaker market has shifted from large floor-standing
stereo speakers in the living room (from ~1950s) to increasingly smaller pairs
of on-stand or shelf speakers, then small multi-channel systems, and finally to
speakers embedded in devices like phones and i-docks, engineers have sought to
get more bass from a given-size driver and box — a pursuit featured in two
papers. Atlantic Technology's
Boaz Shalev
presented details on the HPAS system, an inverted horn with the woofer at the
wide mouth and a port at the narrow throat, which is claimed to deliver more
bass. Ole Wolff's Jeffrey Xia and Lee Guio described an
ultra-compact (~5mm) dynamic driver for earbuds, part of an ongoing race
throughout the industry to shrink dynamic transducers for earbuds, smartphones
and other handheld devices.

For engineers designing docking speaker systems for iPhone 5s,
which use a new ("Lightning") eight-pin connector lacking analog audio
output, Pulsus Technologies' John Oh introduced a new
all-in-one system-on-a-chip to make it relatively painless. For quick
quality-testing of speaker suspension parts, Robert Werner and Klippel showcased
a new Klippel test module that offers effective, robust and simple dynamic
testing of spiders, cones and domes prior to finished-driver assembly.

Dyne Analytics'
Dan Wiggins and
Mark Beach delivered a tutorial on MoTIV, their loudspeaker motor magnetics
modeling software. Using templates for typical motor geometries, magnets,
voicecoils, formers, and other components, MoTIV makes it relatively simple to
design a speaker motor. MoTIV achieves speed and ease of use by sacrificing some
flexibility, but in practice the models come very close to those generated by
more complex, expensive and time consuming programs. Dyne's David Hyre
presented a second paper, on optimizing magnet-structure design for speakers. In
one example, a real driver was compared with a simplified version with the same
critical dimensions (voicecoil, gap and pole piece height, magnet dimensions).

When modeled in MoTIV and in Ansoft Maxwell, the results were
very close (within 2%), demonstrating that simplified driver modeling offers
good accuracy for most applications.

Sonos'
Tim Sheen discussed estimating short-
and long-term power requirements for powered speakers. Using Spice simulation of
an amplifier and speaker playing music, he demonstrated that shorter time
averages (such as instantaneous vs. 100ms averaging) revealed higher peak power
levels.

David Burd (Free Field Technologies;
an MSC Software company) described the Arctran finite-
and infiniteelement acoustical modeling tool. Arctran and similar programs are
complex software tools that are powerful and flexible in trained hands. Computer
modeling must be compared with experimental measurements, driving the models and
reality to converge.

Harman's Director of Business Development and Global
Benchmarking Rob Barnicoat discussed the "Quantum Logic Surround 360" signal
processor, which generates multi-channel sound from mono, stereo or
multi-channel
signal sources. It is said to extract individual voices and instruments as well
as reverberation information, then redirect it into a newly defined
multi-channel
soundfield that can include height information. Equity Sound Investments'
Steve Hutt talked about "Audio System Variance in Production Vehicles". Hutt
measured four identical production vehicles, finding significant variances in
spatially averaged measurements, and wide variances in single point measurements
(not spatially averaged). These are caused by component variations, as well as
by incorrect or damaged speakers or gaskets. Automotive QC groups focus on
quality at the component level (such as speaker frequency response), not at the
system level (what the customer hears from the complete in-vehicle system).
Loudspeaker drivers have a fairly wide performance tolerance, typically ±2dB
and often ≥ ±3dB, which is audible. For non-defective speakers,
equalization can correct much of the problem.

Two half-day seminars were on the design of moving-coil motors
by Richard Little, and design of miniature speakers and microphones by Osman
Isvan:

• Little's "An Overview of Moving-Coil Transducer Motor
Design" provided a review of what makes loudspeaker magnetic motors work, how
they are designed, and how to measure their performance. Once objectives have
been chosen, designing the magnetic motors of moving-coil speakers is a complex
series of tradeoffs involving design topologies; magnet material types and
grades; the permanent-magnet magnetization process; thermal demagnetization;
voicecoil design options; voicecoil inductance; analysis of motor design using
physical equations and finite-element analysis; methods for measuring
magnetic-motor performance; and the general topic of nonlinear motor behavior.
Case studies and examples illustrated each facet of this multidimensional
approach.

• Systems engineer and inventor Isvan addressed "Miniature
Speakers and Microphones: Design and Application", covering digital and analog
topics related to microspeakers and microphones in mobile devices such as
laptops, tablets, cellphones and headsets. He emphasized system optimization for
the particular application. Physical principles apply at any size, yet some
aspects of loudspeaker design don't scale simply. Handheld devices' unique
operating conditions, industrial design, assembly and manufacturing constraints
lead to design and manufacturing approaches that are distinct from
larger-loudspeaker applications. Headphone drivers must be specially designed
and characterized by special test methods, due to their unique acoustic coupling
with the ear. In handsets and headsets, beyond optimization of typical audio
parameters, the two-way communication environment introduces additional
performance metrics such as echo-return loss and doubletalk performance. In
addition, the high density of parts in mobile devices makes induced interactions
among components a challenge. Microphone miniaturization rules out use of a
dynamic microphone, and as the condenser microphone is scaled down, SNR targets
become tougher to meet. Isvan explored omni, unidirectional and noise-canceling
microphones, ECM and MEMS technologies, and compared digital and analog mikes.

Jim Hunter (Klipsch Program Manager, Historian, and 34-year
employee) delivered the keynote: "The Life & Times of Paul Klipsch",
including a slide show of archival documents and photos stretching back to the
1920s as he discussed the life of the prolific inventor and engineer. Audio was
Klipsch's fifth career, which began in 1946 when he founded one of the first
US loudspeaker companies, to build and sell the
Klipschorn

. "It is
difficult to separate the man from the company; however, we can trace the
development of the industry from Edwin Armstrong demo'ing FM with Klipschorns; to
the Audio Fair in New York; to correspondence and visits with Dick Heyser,
Arthur Fiedler, Saul Marantz, Avery Fisher, Sherman Fairchild, John Eargle, and
more." Klipsch is one of America's best known audio pioneers because he
revolutionized the way the world listens to recorded music, having developed the
corner-horn speaker that proved it was possible to reproduce the wide dynamic
range of an orchestra in the home using the very-low-power amplifiers available
in the 1940s. The Klipschorn is the only speaker that has been in continuous
production, relatively unchanged, for over 60 years. Klipsch's audio career
continued up through 2000 when the Journal of
the Audio Engineering Society published one of his last papers. He
died on 5 May 2002, at the age of 98.

At the ALMA banquet dinner, Lifetime Achievement awards were
awarded to Paul W. Klipsch posthumously, and to Vance Dickason (author of the Loudspeaker Design Cookbook and editor of Voice
Coil). The technical contribution award went to Sean Olive for his
research and to Doug Button for his many contributions to transducer design.
Awards for contributions to ALMA were given to Michael Oslac (Board Emeritus)
and Phil Bunch.